First, a set of \( n \) equal resistors of \( 10 \, \Omega \) each are connected in series to a battery of emf \( 20 \, \text{V} \) and internal resistance \( 10 \, \Omega \). A current \( I \) is observed to flow. Then, the \( n \) resistors are connected in parallel to the same battery. It is observed that the current is increased \( 20 \) times, then the value of \( n \) is ______.